This invention relates to plumb bobs.
Plumb bobs have been used since ancient times in construction and other activities for the purpose of locating points in space relative to each other. More specifically, plumb bobs are utilized for locating one point either directly above or below another known point. While perhaps most frequently used alone, plumb bobs have also been components of tools like levels.
A plumb bob may be simply any weight attached to a cord or string, but greatest accuracy can be achieved where the weight terminates in a pointed tip that lies directly below the suspension point when the bob is suspended by its cord. A wide variety of shapes have been used for plumb bobs, but plumb bobs are generally torpedo shaped with a point on one end and a hole through which the cord exits on the other end. Plumb bobs are today most frequently used in building construction, which means that they are frequently carelessly stored in tool boxes, on pickup truck dashboards, and in carpenters' tool belts. As a result, plumb bob points frequently are damaged as a result of the rough handling they receive during storage, and plumb bob cords are often tangled at the same time.
In addition to use in building construction, plumb bobs are useful in metalworking and woodworking shops. One area of utility in such situations is for the purpose of locating the point on a drill press table that lies directly below the axis of rotation of the drill press chuck. This requires the suspension of the plumb bob from the chuck by in some fashion grasping the cord with the chuck. Many drill press chucks will not close enough, however, to grasp a plumb bob cord, with the result that other provisions must be made for grasping the cord in a manner so that it is centered relative to the chuck.